Device for metalizing substrates

ABSTRACT

A wet-chemical treatment system for electrochemically coating flat substrates with coating material, has having a basin for receiving an electrolyte, a transporting means, by means of which the flat substrates can be transported through the electrolyte horizontally, and at least one contact element which comprises a shaft having an axis of rotation and a cylindrical circumferential surface suitable for rolling on the substrate, wherein the circumferential surface comprises at least one electrically insulated segment and at least one electrically conductive segment which can be connected to a current source in such a way that the polarity can be reversed, wherein the axis of rotation of the contact element is positioned above the surface of the electrolyte, and wherein the contact element is designed as a consumable electrode.

The invention relates to a device for metalizing substrates. Inparticular, the invention relates to the field of contact elements usedto electroplate solar cells in the context of a wet-chemical continuous(in-line) treatment system.

STATE OF THE ART AND DRAWBACKS

In the context of producing electronic elements such as e.g. solarcells, substrates made of semiconductor materials such as e.g. siliconrequire an at least one sided coating with conductive materials such ase.g. copper. For this, wet-chemical continuous systems (“inlinesystems”) are used amongst others, by the means of which the substrateslaying on transporting rolls are transported. During transport, thesubstrates are in contact with an electrolyte. For precipitation of themetal contained therein, the substrates are set cathodic.

For producing the electric contact between a current source and thesubstrate, contact wheels are known that roll off on the substrate. Forexample, DE 44 13 149 and DE 198 40 471 A1 disclose electroplatingsystems which use such contact wheels.

It is problematic in this context that not only the substrate but alsothe conductive part of the contact wheel is metalized. Therefore, bothof the aforementioned documents suggest to design the contact wheel in asegmented manner and to de-metalize the contact segment after it hasleft the surface of the substrate by switching the polarity. An improvedsolution for this is known from the letters of patent DE 10 2007 055338. It is suggested to use pairs of contact wheels each mounted on ashaft and triggered in different phases in order to ensure a continuouscoating of the substrate. The contact wheels and the mandatoryconsumable electrodes are completely nested in the electrolyte. In orderto protect the contact wheels from coating, it is suggested to useshielding hoods of insulating material which are each to be mountedbetween contact wheel and consumable electrode.

An alternative solution is e.g. disclosed in EP 0 678 699 B1. However,the sectorless contact rolls as shown therein require auxiliary cathodesand semipermeable membranes to achieve the desired effect thus renderingthe construction complicated; in addition, the necessity for oftenchanging the auxiliary cathodes is a disadvantage.

In practice, realizing durably functioning contact wheels proved to bedifficult.

Another problem is caused by the high floor space requirement of theknown contact wheels resulting in correspondingly voluminous systems.Furthermore, contact wheels that are completely immersed in theelectrolyte require costly solutions for driving the substrates in andout of the system, respectively, because the easily breakable substrateshave to surmount significant height differences.

Also the maintenance of the known systems with the contact wheels asused therein is costly due to the high number of parts.

Finally, practice has also shown that the coating result often is notsufficiently homogenous.

OBJECT OF THE INVENTION AND SOLUTION

The object of the invention is thus to avoid the drawbacks mentionedabove. The invention shall enable a robust and durably functioningelectric contacting of substrates to be metalized in wet-chemicalcontinuous systems with low maintenance requirements. A system designedaccording to the invention shall be smaller than known systems. Themaintenance shall be simplified and the coating result, if possible,shall be improved.

The problem is solved by providing a treatment system according to claim1. Further advantageous embodiments are to be taken from the subclaims,the description and the figures.

DESCRIPTION

A wet-chemical treatment system for the electrochemical coating of flatsubstrates with coating material that is suitable for carrying out theinvention has a basin for receiving an electrolyte and transportingmeans by the means of which the flat substrates can be transportedthrough the electrolyte horizontally. As transporting means,particularly roller-shaped transporting means on which the substrateslay upon, come into consideration. But also clamps at which hangingsubstrates are transported, or string-attached bars onto which thesubstrates lay, are useful as transporting means.

The treatment system further comprises at least a contact element whichcomprises a shaft having an axis of rotation and a cylindricalcircumferential surface suitable to roll on the substrate, wherein thecircumferential surface comprises at least one electrically insolatedsegment and at least one electrically conducting segment that can beconnected with a current source in a manner such that the polarity canbe reversed. Accordingly, the contact element serves to electricallycontact a substrate for its electrochemical treatment (coating). Theelectric contact between the current source and the substrate is onlyestablished when the latter is touched by the electrically conductivesegment. Since the circumferential surface during the continuoustransport of the substrate rolls off on the same, the conductive and theinsolated segment interchange with respect to each other.

The central angle of the electrically conductive segment preferably isbetween 90° and 270°, with an angle of 180° being particularlypreferred. The remaining part of the circumferential angle is attributedto the electrically insolated segment.

While the conductive segment during its contact with the substrate isswitched cathodic and thus enables a coating of the substrate, it isswitched anodic upon non-contacting the substrate resulting in ade-metallization (“de-coating”) of the segment. In this manner, thethickness of a possible layer of coating material undesirablyprecipitated onto the segment is reduced rather than enlarged with a netprecipitation of coating material being zero. With central angles of theelectrically conductive segment deviating from 180°, it is advantageousto optimize the de-coating performance by adapting e.g. the currentstrength or the speed of rotation.

According to the invention, the axis of rotation of the contact elementis positioned above the surface of the electrolyte. This means, that atleast half of the circumferential surface of the contact element isoutside the electrolyte. Contrary to what is known from the state of theart, the contact element is not completely immersed in the electrolyte.Nevertheless, a de-coating is possible because the circumferentialsurface upon rotation drags some electrolyte and does not dry outquickly such that the anodic switch of the electrically conductivesegment results in delivering of the coating material, which e.g. iscopper, to the electrolyte.

Preferably, the distance between the axis of rotation and the substrateside to be contacted running in parallel thereto is 80% to 100% of theradius of the circumferential surface. This means, that only a smallpart of the circumferential surface is positioned within theelectrolyte, with only a line touching between circumferential surfaceand surface of the electrolyte being possible in boarder case conditions(100%). In this case, the substrate must be transported immediatelyalong the surface of the electrolyte, while in other cases it may laycorrespondingly lower. Particularly preferred, the said distance isdimensioned such that at least the shaft and possibly its bearings arepositioned outside the electrolyte, if they are not arranged beyond thebasin wall, because in such a case there is no danger of damage fromaggressive media anyway.

Such a treatment system has the advantage that, due to the arrangementof the typically plurality of present contact elements essentiallyoutside of the electrolyte, it is more robust and durably functioningand requires less maintenance. The reason for this lies in the avoidanceof problems encountered with systems of the art with regard to thebearing and sealing of the contact elements within the electrolyte. Themostly aggressive media do no longer or only to a minor extent come intocontact with the bearings, resulting in an improved operational lifespan and a simpler construction of the same.

A further advantage is that a substrate, irrespective of the diameter ofthe contact element being present there above, has to be guided to alesser extent below the surface of the electrolyte.

According to the invention, the contact element is furthermore designedas a consumable electrode. This means, that it is at least partly madeof coating material such that upon corresponding polarity itcontinuously delivers coating material to the electrolyte which thendeposits onto the substrate.

The advantage of a contact element designed as consumable electrode isthat a system comprising such contact elements can be configuredsignificantly smaller because parts are left out.

As soon as the consumable electrode has delivered the major part of itscoating material to the electrolyte, it may either be replaced or it maybe regenerated by cathodic polarity while simultaneously feeding newcoating material which e.g. is introduced into the system or transportedthrough the same in the form of substrate-shaped plates.

By permanently coating and de-coating the consumable electrode, i.e. theelectrically conductive parts of the contact element, an oxidation ofthe same is/are avoided effectively such that a stable process withuniform deposition is achieved.

According to a preferred embodiment, the contact element is designed asa pipe or rod made of coating material, e.g. of copper, and has anelectric insulation layer along at least one longitudinal section of itscircumferential surface destined for contacting the substrate. However,this insulating layer may also extend to longitudinal sections notdestined to contact the substrate, if this is constructivelyadvantageous.

Constructively, this embodiment may be realized particularly easy andcost-effective.

According to another embodiment, the contact element is designed as oneor several discs being arranged on the shaft which is designed as pipeor rod.

In the case of an essentially pipe- or rod-shaped contact element it ispreferred that the insulating layer is designed as plastic part whichcan be attached to the circumferential surface and partly covers thesame. The attachment may be effected along the longitudinal axis(sliding on) or it can be clipped-on laterally. If the central angle ofthe insulating segment is smaller than ca. 190°, it is clear thatmeasures are needed to hold the insulating layer at the pipe or rodbecause otherwise it would fall off. Such measures may e.g. be sectionswith enlarged central angle which are then located at positions beingoutside of the substrate track. But also plastic pins which interactwith corresponding holes being introduced in the pipe- or rod-shapedshaft may serve to fasten. Preferably, the insulating layer may be usedagain.

According to a further embodiment, the shaft of the contact element at afree longitudinal or end section not destined for contacting thesubstrate has a wiper contact surface that rotates with the shaft inorder to provide a connection to the current source whose polarity canbe switched/reversed. This wiper contact surface interacts withcorrespondingly positioned, preferably fixed pins or the like whichthemselves are connected with the poles of the current source and arepreferably arranged outside the electrolyte.

The wiper contact surface preferably is designed disc-shaped having twoarc-shaped contact strips which are configured to correspond to thesegments arranged at the circumferential surface. This means, that theirangle of the arc correspond to the two central angles of the segmentsand are arranged such that a reverse of the polarity just happens whenthere is a segment change at the substrate surface. It is clear, thatboth contact strips are connected with the electrically conductivesegment.

It is particularly preferred that the wiper contact surface is arrangedcompletely outside the electrolyte. This can e.g. be achieved byproviding a corresponding passage in the wall of the basin through whichthe shaft can be guided. Thus, no problems caused by aggressive mediaoccur at the wiper contact surface. If the shaft has a significantlysmaller diameter than the circumferential surface, it is also possibleto guide the shaft above the rim of the basin to the outside of thebasin, or there is enough place between the lowest point of the wipercontact surface and the surface of the electrolyte such that one has notto fear any liquid contact.

According to a further embodiment, the contact element is also aholding-down means to avoid floating of the substrates. In other words,the contact element is designed and arranged in such a manner that itavoids the flat substrate to float and leave the transportation track.Holding-down means are known in the art but they are exclusively used toguide the substrates, not for electric contacting.

In this way, components can again be omitted resulting in a smaller andmore cost-effective construction.

According to another embodiment that can be combined with the aboveembodiments, the contact element is also a roller-shaped transportationmeans. In other words, the substrate lays on additional contact elementswhich then are positioned underneath the same in the electrolyte andwhich upon rotation provide a continuous transport of the substratethrough the basin.

Also by this, mounting parts, particularly separate transporting rolls,can be omitted also resulting in a smaller and more cost-effectiveconstruction.

In certain cases the exchange of the electrolyte in the regionunderneath the substrate—in particular when contact elements are presentthere—may not be completely satisfying such that a non-sufficientlyhomogenous coating develops at the substrate underside. Accordingly, afurther embodiment provides flush nozzles arranged within theelectrolyte for continuously streaming the electrolyte against thoseparts of the contact element that are also arranged within theelectrolyte.

In other cases it may occur that the wetting of the contact elementduring the phase in which the electrically conductive segment is outsidethe electrolyte as mentioned above is not completely satisfying.Therefore, a further and preferred embodiment provides flush nozzleswhich are arranged outside the electrolyte, i.e. above its surface, inorder to continuously wet those parts of the contact element with theelectrolyte which are also outside the electrolyte. In other words, theflush nozzles eject the electrolyte from the basin and/or e.g. from aseparate reservoir in direction of the contact elements such that theseare to a large extent completely wetted. In this manner, theconstruction can be kept simple as described above without questioningthe success in de-metallization.

The present invention solves the problems known in the art in a simpleand effective manner. It provides a robust and durably functioningelectric contacting of substrates to be metalized in wet-chemicalcontinuous systems with low maintenance requirements. A system accordingto the invention is smaller than known systems. Maintenance issimplified and the preferred embodiment of the invention improves thecoating result.

DESCRIPTION OF THE FIGURES

In FIG. 1 the invention is exemplified schematically.

A flat substrate 1 in the form of a solar cell is arranged in anelectrolyte (not shown). Its upper side is touched by a contact element2, i.e. by an electrically conductive segment 3A of the same. Thecircumferential surface of the contact element 2 as shown serving totouch the substrate 1 is disc-shaped, although it can also becylindrical according to an embodiment not shown.

Opposite to the electrically conductive segment 3A, an electricallyinsulated segment 3B is arranged.

The contact element 2 has a shaft 4 with an axis of rotation 5 aroundwhich the contact element 2 and in particular the circumferentialsurface can rotate (arrow 7). The conductive components being in contactwith the electrolyte (conductive segment 3A, shaft 4) consist at leastpartly of a material that is suitable for consumption and thus representa consumable electrode. As shown, an additional consumable electrode 12that is separate from the device according to the invention andelectrically connected with the current source 6 is arranged in theelectrolyte, although it can be omitted advantageously according to apreferred embodiment not shown.

At an end section 8 not destined for contacting the substrate 1 thecontact element 2 has a wiper contact surface 9 which rotates with theshaft 4 to generate a connection with the current source 6 in such amanner that the polarity can be reversed. This wiper contact surface 9is preferably completely, but at least partly arranged outside of theelectrolyte, and interacts with correspondingly arranged wiper contacts10 which themselves are connected with the poles of the current source6.

The wiper contact surface 9 as shown is designed disc-shaped and has twoarc-shaped contact strips 11A, 11B which are designed in correspondencewith the segments 3A, 3B being arranged at the circumferential surface.This means that their angles of the arc correspond to the two centralangles of the segments 3A, 3B and are arranged such that a switching ofpolarity just happens when there is a segment change at the substratesurface. It is clear, that both contact strips are connected with theelectrically conductive segment 3A which, as shown, can be achieved viathe shaft 4.

The contact strip 11A thus provides the contact region for thede-coating of the contact element, and the contact strip 11B serves ascontact region for the coating of the substrate. Not shown areelectrical connections from the contact strips to the conductive part ofthe circumferential surface or to the shaft, respectively.

REFERENCE LIST

-   1 Substrate-   2 Contact element-   3A Electrically conducting segment-   3B Electrically insolated segment-   4 Shaft-   5 Axis of rotation-   6 Current source-   7 Arrow-   8 Longitudinal or end section not destined for contacting-   9 Wiper contact surface-   10 Wiper contact-   11A Contact strip-   11B Contact strip-   12 Consumable electrode

1. A wet-chemical treatment system for electrochemically coating flat substrates (1) with coating material, with a basin for receiving an electrolyte, a transporting means, by means of which the flat substrate (1) can be transported horizontally through the electrolyte, and with at least one contact element (2) which comprises a shaft (4) having an axis of rotation (5) and a cylindrical circumferential surface suitable for rolling on the substrate (1), wherein the circumferential surface comprises at least one electrically insolated segment (3B) and at least one electrically conductive segment (3A) which can be connected to a current source (6) in such a way that the polarity can be reversed, wherein the axis of rotation (5) of the contact element (2) is positioned above the surface of the electrolyte, and wherein the contact element (2) is designed as a consumable electrode.
 2. The treatment system according to claim 1, wherein the contact element (2) is designed as a pipe or rod of coating material and has an electrically insolating layer along at least one longitudinal section of its circumferential surface destined for contacting the substrate (1).
 3. The treatment system according to claim 2, wherein the insolating layer is designed as a plastic piece which can be mounted on the circumferential surface.
 4. The treatment system according to claim 1, wherein the shaft (4) of the contact element (2) at a longitudinal or end section (8) not being destined for contacting the substrate (1) has a wiper contact surface (9) for its commutatable connection to the current source (6).
 5. The treatment system according to claim 4, wherein the wiper contact surface (9) is positioned completely outside of the electrolyte.
 6. The treatment system according to claim 1, wherein the contact element (2) is a holding-down means to avoid the substrates (1) to float.
 7. The treatment system according to claim 1, wherein the contact element (2) is a cylindrical transporting means.
 8. The treatment system according to claim 1, wherein flush nozzles are positioned within the electrolyte for the continuous flow of the electrolyte against those parts of the contact element (2) which are also positioned within the electrolyte.
 9. The treatment system according to claim 1, wherein flush nozzles are positioned outside the electrolyte for the continuous wetting of those parts of the contact element (2) with the electrolyte which are also positioned outside the electrolyte. 